204 REPORT OF BOARD OF CONSULTING ENGINEERS, PANAMA CANAL.


one-third -of a mile from the canal; this darn will be erected on rock f oundations between the Cerro Obispo and the Cerro Santa Cruz, and will consist of a structure made of concrete reenf orced with embedded steel, designed to hold back the waters at an altitude of 200 feet above the sea.
 The Bohio dam is placed across the valley of the Chagres on the South American side of the canal. It will consist of a huge dump of clayish sand to be deposited by hydraulic miethods across the valley of the Chagres to a thickness of 2,500 to 3,000 feet at the foot of the embankment, with very easy slopes on the water side of the dam, and a thickness at the top of 1,200 feet.'
 The spillway of the lake will he placed on the other side of the canal (thereby eliminating all possible contact of the dam with an accidental current), in one of the saddles which canl be found in the chain of hills connected with the Bohio Hill, either in the saddle I indicated on my plans of 1892 or in the Rio Gigante saddle, which was selected by both the Comit6e Technique and by the Isthmian Commission in its report of 1901.

 AUTOMATIC REGULATION OF LAKE BOHIO.
 The spillway will be a weir, pure and simple, the crest of which will be at 50 feet above sea level (15.25 in.). The maximum height of the lake being at elevation 60 feet (18.3 i.), the weir will have such a length as to discharge about 140,000 cubic feet, or 5,000 cubic meters, per second, at the maximum elevation of the lake. A weir of 525 meters (1,75 ft.) in length will dispose for an indefinite period of a flood higher and of longer duration than any ever known.
 These are the conditions of automatic regulation of the Bohio Lake which were adopted by the Isthmian Canal Commission in its report of 1901, and I think they cover all possible eventualities at Bohio with a marvelous simplicity. The Comit6" Technique adopted the objectionable feature of gates opening below the minimum level, to dispose more quickly of the water at low stage, but this is a dangerous disposition which should not be admitted.
 As will be seen later on, the maximum amount of water disposed of by the weir will be normally 1,000 cubic meters (33,000 c: f.) a second, even if the greatest flood ever known, that of 1879, should be reproduced with double intensity or duration at Gamboa.

ADVANTAGES OF THE CHANNEL SELECTED FOR LEADING TO THE SEA THE CHAGRES FLOODS BELOW BOHIO.
 The channel between the sea and the spillway of the Bohio Lake is, like this system of regulating the lake, an ideal element of the solution. It is the bed of the River Chagres itself, which will constitute the derivation for nearly its entirety. Two artificial beds only have to be dug, one between kilometers 16 and 22 and another between kilometers 8 and 10. The latter is open already and needs only widening.
 The extreme simplicity which results from the selection of this side of the canal is obvious. The bed of the river is wide and deep, and by natural accretion it has spontaneously deposited earth on its banks which forms, as it were, two natural embankments, preventing the overflow. It must be remarked, also, that according to what I established in my book of 1892 (p. 156),,the reduction in the length of the river between Bohio and the sea, due to the short cut opened between kilometers 16 and 22, will allow the Chagres to dispose of a flood of 1,000 cubic meters as it disposes to-day of a flood of 850 cubic 'Meters, which is a very small, ordinary wet-season freshet, without any overflow out of the bed of the river.
 I proposed this solution, which is one of the great advantages of the Bohio Lake, in my plans of 1892. For a reason which I ignore, it was not adopted by the Comit6" Technique in 1898, which provided for two deviations below Bohio, one on each side of the canal; but it has been taken up again since by the Isthmian Canal Commission in its report of 1901 and forms a characteristic feature of the project they adopted.


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